Isotype-associated recognition of allergen epitopes and its modulation by antigen dose.

The existence of competing and blocking IgG antibodies and their interrelationship with IgE antibodies was investigated in the IgE immune response of CBA/J mice to bee venom phospholipase A2 (PLA2) and keyhole limpet haemocyanin (KLH). Minute doses of antigen induced high titres of both IgE and IgG antibodies, whereas large doses elicited high IgG responses but only weak IgE antibody titres. Immunization with minute doses of antigen led to the production of antibodies with class-associated epitope specificities (designated epitopes G for IgG and E for IgE antibodies), and therefore no competition was observed. For IgG antibody production, G epitopes were immunodominant and IgG antibodies directed to E epitopes were produced only after immunization with an increased immunogen dose. Under this condition IgG antibodies recognizing the E epitopes acted as blocking antibodies competing with IgE antibodies for binding to E epitopes, the immunodominant epitopes for the IgE response. The data demonstrate the existance of distinct immunodominant antigenic determinants for IgE and IgG antibodies on PLA2.